I agree that they look a little too high. It looks like they are too spindly, currently, and also a little like you are trying to game for a better shot. Cut down the height, or add some stuff underneath so it looks more like it’s naturally been built up that high.
I would suggest trying to fit the assault cannons onto the current razorback turrets. Of course that assumes that you have spare turrets. I agree that it is too high. I would also suggest something to cover the space above the top of the guns.
I’m scratching building because of the lack of turrets indeed!
I was planning on lowering them all the same and have done so and what I’m aiming to do is magnetise the guns so they sort of hang off the top of the ‘box’ aspect. I’ll be adding ammoboxes, chapter symbols and rivets once I get the shape of it down right. I’ve currently sanded down the edges so it isn’t a literal box and will post up some pictures soon hopefully. I need to get access to some wiring though to fill out the bottom.